The present invention relates to an imaging device, and more particularly to a single-chip color video camera which employs one solid-state image sensor.
At present, a single-chip color video camera which produces color video signals with one solidstate image sensor has been put into practical use. In such a camera, several kinds of color filters having different transmission light characteristics are disposed in cyclic correspondence with the respective picture elements (photoelectric conversion elements) of the solid state image sensor, to obtain a plurality of chrominance signals. Accordingly, the spatial sampling frequency of each chrominance signal is lowered to several tenths of the sampling frequency of the picture elements, and a colored moire pattern is prone to appear.
A method of lessening color moire patterns from a single-chip color video camera is described in Japanese Patent Application Laid-open No. 54-131819 and U.S. Pat. No. 4,153,912 corresponding thereto.
With this method, operations to be stated below are performed. By way of example, when color filters shown in FIG. 1 (in which letters R, G and B denote color filters transmitting red, green and blue, respectively) are combined so that the individual filter elements are held in one-to-one correspondence with the picture elements of the solid-state image sensor, signals illustrated in FIG. 2(a) are obtained. The signals are separated to obtain a red signal, a green signal and a blue signal (hereinbelow, abbreviated to "R, G and B signals" respectively) shown in FIGS. 2(b)-2(d), in which by way of example, at a time t.sub.1, the R signal is obtained but the G and B signals are not obtained, and at a time t.sub.2, the G signal is obtained but the R and B signals are not obtained. Therefore, at the time t.sub.1 by way of example, the magnitudes of R.sub.0 and R.sub.2 are compared with the magnitude of R.sub.1 to determine which of the magnitudes is closer to the magnitude of R.sub.1, and the G signal and the B signal are interpolated with G.sub.0 and B.sub.0 respectively when R.sub.1 is closer in magnitude to R.sub.0 or when R.sub.1 is close both to R.sub.0 and R.sub.2, and are interpolated with G.sub.1 and B.sub.1 respectively when R.sub.1 is closer in magnitude to R.sub.2 or when R.sub.1 is close neither to R.sub.0 nor to R.sub.2. When the R, G and B signals are interpolated by such operations, three signals of high sampling frequency and uniform phase as shown in FIGS. 2(e)-2(g) are obtained. As a result, signals to be originally derived are interpolated substantially correctly at the boundary parts of a subject (object) having a sufficient size as compared with the interval of the picture elements, and the colored moire pattern to appear at the boundary parts are relieved.
However, regarding a subject having a moire pattern which varies in a range several times larger than the interval of the picture elements, the original signals cannot be correctly interpolated, and there is the problem that the colored moire pattern increase conversely.
By way of example, when bright and dark subjects are focused on the color filters shown in FIG. 1 in correlations shown in FIG. 3, signals shown in FIG. 4(a) are obtained. When they are separated into R, G and B signals which are then subjected to the processing of the prior art stated above, signals in FIGS. 4(b)-4(d) are obtained. When these signals are compared with the circumstances of the subjects in FIG. 3, the B signal at a time t.sub.4, the G signals at times t.sub.6 and t.sub.7, and so on are obviously different from signals to be originally derived. As a result, signals produced as if a blue subject were imaged are obtained at the time t.sub.4 by way of example, and there is the problem that the false color appears on a reproduced picture.